The present invention is a braking system for applying the brakes of a towed vehicle in tandem with the brakes of a towing vehicle.
Those who travel by motor home sometimes wish to tow an automobile. In this situation, which represents the most typical application of the present invention, it is generally desirable for the towed automobile to brake in tandem with the motor home. A number of approaches have been developed to achieve this cooperative braking.
One type of towing/towed vehicle braking system is known as a surge brake system. A surge brake system senses any forward pressure of the towed vehicle against the hitch that couples the vehicles together and applies the brakes of the towed vehicle in response. Although a surge brake system has the appeal of simplicity, it is fraught with problems. First, if the towing vehicle attempts to move backwards, a surge brake system will sense a resisting forward pressure by the towed vehicle against the hitch and apply the brakes in response to this pressure. As a result, in order for the coupled vehicles to move backwards the surge brakes must be disabled, typically manually at the hitch. The task of disabling the surge brakes is difficult to accomplish quickly, making an unexpected demand to travel in reverse extremely problematic. Second, if the coupled vehicles are moving over a hilly or curvy road, the surge brake system is likely to jolt the vehicles. This is because every time the driver takes his foot off the brake pedal of the towing vehicle there will be a moment when the brakes of the towed vehicle remain activated due to the lag time of the mechanical surge brake system. When the towed vehicle brakes are released the occupants will feel a forward jolt if the driver has switched quickly from brake pedal to accelerator.
Another system that is similar to the surge braking system has an accelerometer in the towed vehicle that applies the brakes in response to deceleration. An accelerometer-driven brake system suffers from the same problems encountered with a surge brake system.
Another type of towing/towed vehicle braking system uses a sensor under the brake pedal of the towing vehicle that is operatively connected to an actuator for depressing the brake pedal of the towed vehicle. Towing vehicle brake pedal sensor systems are difficult to install because the brake pedal portion of the cab of a typical motor home is fairly inaccessible to a technician. Additionally, the sensor is a nuisance to the driver as it is directly under the brake pedal, where it may easily be kicked.
Yet another type of towing/towed vehicle braking system includes a device for measuring the towing vehicle brake fluid pressure. The fluid pressure measuring device is operatively connected to an actuator that is interposed into the hydraulic braking system of the towed vehicle and applies pressure directly to the brake fluid of the towed vehicle in proportion to the towing vehicle brake fluid pressure. The braking signal is communicated from the towing vehicle to the towed vehicle by means of vacuum differential. Systems having an actuator interposed into the towed vehicle hydraulic system are so difficult to install that one manufacturer requires installation at its own factory.
Therefore, what is needed but not available is a system that is both easy to install and effective at causing the braking system of a towed vehicle to operate in tandem with the braking action of a towing vehicle.